Integrated circuit chips and other circuitry components can be coupled to each other and to other circuits in compact modules, units and packages. For example, several monolithic microwave integrated circuits (MMIC's) in chip form can be packaged to provide a unit capable of operating at microwave and millimeter wave frequencies. Advancements in GaAs MMIC's, and in particular, those which operate in the millimeter bands, have made it especially critical that connections with such chips, particularly RF connections, be of the highest quality. That is, interconnections must be made consistently such that they provide good impedance match between the MMIC and the means of transmission, and the connections themselves must be reliable.
Each MMIC chip may contain several microwave or millimeter wave circuits such as amplifier, converter or oscillator circuits depending on the function and level of integration. For interfacing both DC and RF signals and currents a MMIC chip has contact pads on one surface, typically around the perimeter of the top surface, which are connected by internal conducting lines to various portions of the actual circuits within the chip. In the case of RF connections between circuits within a chip, either microstrip or coplanar waveguides are used to form waveguide transmission lines. Chips that use internal microstrip transmission lines typically have a conducting ground plane on the bottom surface of the chip in opposing relation to the transmission lines.
Existing MMIC packages typically utilize a chip carrier, sometimes called a motherboard, designed to support one or more MMIC's. The chip carrier has a conducting ground plane on one surface and thin film metallization patterns disposed on the opposing surface providing DC and RF interconnections among the MMIC's and between the MMIC's and package input/output terminals. The RF interconnects serve as waveguide transmission lines employing such techniques as microstrip or coplanar fabrication.
In such existing MMIC packages, MMIC chips are mounted on the chip carrier, typically in recesses in the carrier surface, and interconnections between contact pads on the chip surface and interconnect metallizations on the chip carrier are made by bonding wires or ribbons. In some existing MMIC packages, longer interconnects are made by miniature coaxial cable. In another packaging method, known as waffle line, the chip carrier is made of metal having a waffle shaped surface (two-dimensional grooves cut into metal). This metal surface acts as a ground plane; flat areas are created in locations where chips and other circuit components are to be mounted. DC and RF interconnections are made by bonding insulated wire to chip contact pads. The wires carrying RF signals are pressed into and routed through the waffle line grooves to provide shielding similar to the outer conductor of a coaxial cable.
Packages for chips operating at lower frequencies or DC (digital chips, for example) can utilize interconnect methods similar to those employed with MMIC chips but may not require the chip carrier to have a ground plane surface when waveguide transmission is not employed.
In all of the existing interconnection methods discussed, wire, ribbon or cable must be bonded to chip contact pads, a process in which each connection must be made either directly by hand or indirectly by an operator guiding a bonding machine. As can be appreciated, manually making such interconnections is labor intensive and time consuming resulting in higher production costs. Furthermore, because of the extremely small dimensions involved, repeatability of reliable interconnections is difficult to achieve leading to inconsistent and less than optimum impedance matched interconnects and thus to performance variations between otherwise identical packages. An additional disadvantage of existing packaging techniques is that the chip carrier only provides one level (the carrier surface) for DC and RF interconnection networks and for mounting peripheral circuit components such as chip capacitors. If crossovers of DC and/or RF interconnections are required, then extra wire bonding must be used.
Consequently, a need has arisen for more consistent and less labor intensive packaging techniques for circuitry components to increase repeatability, to provide more than one circuit level for interconnections and placement of peripheral components, and to decrease the production cost of functional modules